1.

5 Transport systems
Objectives

By the end of the subtopic, learners should be able to:

 Describe osmosis and diffusion in plants.

 Demonstrate the movement of water in plants.

 State the components of blood.

 State the function of each of the components of blood.

Diffusion and osmosis

1. Diffusion

 In everyday life, perfume sprayed in one corner of the room can be smelled by
someone in the other corner as the gaseous particles move by diffusion across
the room.

 Substances need to move in organisms from one place to another.

 Most of the substances are in a dissolved state and they have to pass through
the cell membrane.

 Diffusion is one of the passive methods by which substances can enter or leave
the cell.

 Passive means that the process does not need or use energy for it to occur.

 Diffusion can be defined as the process whereby particles move from a region
where they are in high concentration to a region where they are in low
concentration.

 For diffusion to take place there must be a concentration gradient.

 This means that there must be a difference in concentration of the particles that
are moving.

 For example, oxygen can diffuse through cell membranes and if there is a higher
concentration of oxygen outside the cell than inside the cell, oxygen molecules
diffuse into the cell.

 In the diagram in Fig 1.5.1 there is a demonstration of diffusion. In container A

the particles are concentrated at one place and in container B the particles have
moved throughout the liquid by diffusion.
 Container A Container B

Fig 1.5.1: A diagram showing diffusion in a liquid.

Diffusion of a solid in a Liquid:

Experiment: To demonstrate diffusion in liquid.

Materials

 Beaker

 Potassium permanganate or copper sulphate crystals

 Water

Procedure

1. Fill the beaker to three quarters full with water.

2. Drop some crystals of copper sulphate or potassium permanganate carefully

without disturbing the water.

3. Observe the crystals as they slowly dissolve

Expected Observations

 The water gets uniformly coloured after some time,

 Blue in case of copper sulphate and Pink in case of potassium permanganate.

Conclusion

 The molecules of the chemicals diffuse gradually from higher concentration to

lower concentration and are uniformly distributed after some time.

 The copper sulphate or potassium permanganate diffuses independently of

water.

Diffusion of Liquid in Liquid:

Experiment: Diffusion of a liquid in a liquid

Materials

 Two test tubes

 Chloroform

 Water

 Ether

Procedure

1. Add 30mm depth of chloroform to one test tube and 4mm depth of water in the
other.

2. Now to the first test tube add 4mm depth of water and to the other add 30mm
depth of ether (both chloroform and ether form the upper layer).

Caution: Ether must be added carefully to avoid disturbing the water.

3. The tubes are closed tightly with cork stoppers.

4. Mark the position of liquid layers in each test tube and measure the thickness of
each layer.

5. Set aside the tubes for some time and record the thickness of the liquids in each
test tube at different intervals.
Expected Observations

 The rate of diffusion of ether is faster than that of chloroform into water as
indicated by their respective layer thicknesses.

Conclusion

 Substances having higher molecular weights show slower diffusion rates than
those having lower molecular weights.

Experiment: To show diffusion of a gas in a gas

Materials

 Two gas jars

 Carbon dioxide and oxygen gases

Procedure

1. Fill one gas jar with carbon dioxide. (Either by laboratory method: calcium
carbonate plus hydrochloric acid or by allowing living plant tissue to respire in a
closed jar).

2. Fill another jar with oxygen (either by laboratory method: manganese dioxide plus
potassium chlorate, or by allowing green plant tissue to photosynthesize in a
closed jar).

3. Invert the oxygen jar over the mouth of the carbon dioxide jar and make it air-tight
with grease.

4. Allow to remain for some time.

5. Carefully remove the jars and test with a glowing match stick.

Expected Observations

The glowing match sticks flared up in both the jars.

Conclusion

The diffusion of carbon dioxide and oxygen takes place in both the jars until the
concentrations of the gases are the same in both gas jars making a mixture of carbon
dioxide and oxygen.
2. Osmosis

 This is the movement of water molecules from a region of higher water

concentration to a region of lower concentration through a selectively permeable
membrane.

 This is a special kind of diffusion that moves water molecules from a place of
higher concentration to a place of lower concentration to create a stable and
equal cellular environment.

 Osmosis is a vital function to the growth and stability of plant life.

 Without osmosis, photosynthesis would never occur and plants would wilt and
die.

 Osmosis distributes water through selectively permeable membranes to

maintain this proper volume and pressure of all plant cells.

 Plant cell walls are incredibly tough and rigid which is necessary to uphold the
integrity of the cell.

 Fig 1.5.2 shows osmosis.

 Water moves from the fresh water to the solution.

 This is because there is a lesser concentration of water in the salt solution.

Fig 1.5.2: Demonstration of osmosis

 When the concentration is the same on both sides of the membrane, the
movement of water molecules will be the same in both directions.
  At this point, the net exchange of water is zero and there is no further change in
the liquid levels.

Movement of water in plants

 Most plants obtain the water and minerals they need through their roots.

 The path taken by water in plants is from the soil to roots, stems and finally the
leaves.

 Xylem vessels conduct the water up the plant.

 Dissolved minerals travel in the water (often accompanied by

various organic molecules supplied by root cells).

 Transpiration caused by the evaporation of water at the leaf creates negative

pressure (tension) at the leaf surface a process called transpiration pull.

 Water from the roots travels up the plant by transpiration pull.

 At night, when stomata close and transpiration stops, the water is held in the stem
and leaf by the cohesion of water molecules to each other and the adhesion of
water to the cell walls of the xylem vessels.

Experiment: To demonstrate water uptake by plants

Materials

 Peeled potato

 Petri dish

 25% sucrose solution

 Pin

Procedure

1. Scoop a cavity in a large sized peeled potato.

2. Slice the bottom of the potato to make the base flat.

3. Keep this potato in a petri-dish containing water, in such a way that half the
potato is immersed in water.

4. Fill the potato cavity with 25% sucrose solution and mark its level by inserting a
pin as shown in the diagram below.
 Fig 1.5.3: Osmosis in a potato

Expected observations

 After some time, the liquid in cavity rises, because, the water (pure solvent) has
moved through the potato walls and accumulated inside the cavity.

Conclusion

 This experiment proves that osmosis has taken place. Potato wall acts as
selectively permeable membrane.

 This proves that the water molecules move from high concentration to the low
concentration.

The blood

 It is the red fluid that circulates in the heart, arteries, capillaries, and veins of animal
carrying food and oxygen to and removing away carbon dioxide and other waste
products from all parts of the body.

 It provides the body with nutrition, oxygen, and waste removal.

 Blood is mostly liquid, with numerous cells and proteins suspended in it.

 The average person has about 5 litres (more than a gallon) of blood.

Components of blood

a. Plasma

 It is the liquid part of blood excluding all cells and platelets.

 Plasma transports substances through the blood, and perform other functions.

 Blood plasma also contains glucose and other dissolved nutrients.

  Plasma provides the environment for the transportation of platelets to the
needed places.

b. Red blood cells

 These function to transport oxygen around the body.

 They lack nuclei and are biconcave disc shaped.

 These cells contain a red pigment called haemoglobin.

 Haemoglobin is made up of iron and its transports oxygen around the body.

 The diagram below shows red blood cells.

Fig 1.5.4: Red blood cell

c. White blood cells

 These are the cells of the immune system that are involved in protecting the
body against infectious disease and foreign invaders.

 The diagram in Fig 1.5.5 shows different types of white blood cells.

 Unlike red blood cells, this type of a cell contains a nucleus.

Fig 1.5.5: Different types of white blood cells

d. Platelets

 Platelets are tiny cell fragments that circulate through our bloodstream.

 Their role is to help stop bleeding when there is an injury to our body.

 They are responsible for blood clotting during an injury, which stops further blood
loss and prevents entrance of pathogens.

 Fig 1.5.6 shows an artery with red blood cells, white blood cells and platelets.

Fig 1.5.6: A blood vessel with the blood components.